checkout improvements

What's changed

• Cache South African suburb data locally and refresh it daily for faster searches.
• Allow suburb searches without a minimum character count.
• Remove the search delay and the town/suburb search toggle.
• Improve the suburb search field layout in WooCommerce Blocks checkout.
• Reorder classic checkout address fields, placing email before location type.
• Fall back to the Collivery API when the suburb cache is unavailable.